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Daniel Kaping, Paul Duhamel, Michael A. Webster; Adaptation to natural facial categories. Journal of Vision 2002;2(10):128. doi: https://doi.org/10.1167/2.10.128.
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© ARVO (1962-2015); The Authors (2016-present)
Variation in faces are often judged and classified in terms of discrete categories (e.g. identity, gender, and emotional expression). We examined how the boundaries defining these categories can be influenced by prior adaptation to images within a given category.
Stimuli were frontal-view images of faces taken from the Ekman and Matsumoto image set. Pairs of faces were morphed (Gryphon Morph v 1.5) to form a finely graded series of images that varied between genders, expressions, or ethnicities (Caucasian and Japanese).
Images at different levels along the morph were varied with a 2AFC staircase to define the category boundary at which the two category judgments were equally likely. Observers made settings before or after adapting to one of the two original faces. Adaptation produced strong shifts in category boundaries toward the adapting image, so that the original neutral point appeared biased away from the adapting image and thus toward the second, more novel image. For example, after adapting to a male face or an expression of surprise, a face that was previously judged to be neutral was rated as female or happy, respectively. Our results suggest that measurable aftereffects can rapidly occur for natural and common variations in faces, suggesting that adaptation may routinely influence face perception in everyday viewing. Measurements of the category boundaries before adapting to the category exemplars also revealed significant differences between individuals within different categories. For example, females select a gender boundary that is shifted toward the female face, relative to males. Thus observers may be sensitive to how faces differ from their individual norm.
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